1. Field of the Invention
The present invention relates to a process for applying a defined surface roughness to a metal strip. More specifically, the present invention relates to a process for applying a defined surface roughness to a steel strip that is cold rolled in at least one reversing roll stand and coiled for preventing sticking of strip during subsequent annealing in a hood-type or bell-type annealing installation following the reversing roll stand. In addition, a temper rolling stand for at least one planishing or flattening pass is associated with the bell-type annealing installation.
2. Description of the Related Art
Reversing cold rolling mills for producing large tonnages of cold-rolled strip have been extensively replaced by tandem mills comprising multiple stands in which a greater tonnage of strip is more economically rolled. Lately, smaller-production rolling mills, also known as minimills, are increasingly being designed. These minimills are set up in a more customer-oriented manner for economical rolling operations specifically geared to small tonnage production. Reversing cold rolling mills were and are well suited for minimills because investment costs for a rolling mill outfitted with only one or two reversing cold rolling stands are in balance with the quantity of commercial products rolled on such a mill.
In the cold rolling of metal strip and subsequent annealing of the coiled metal strip in bell-type annealing installations, the surfaces of the blank or smooth metal strip contacting each other in tight coils in the bell-type annealing installation may stick together. When this occurs, the overall production process is considerably impeded and may lead to the disposal of the strip. Therefore, the potential for the tightly coiled strip to stick together must be minimized or prevented. In prior-art tandem mills having a plurality of roll stands arranged successively in a line as well as in prior art reversing rolling mills, the sticking problem was solved in that the surface of the strip was roughened prior to the annealing process. In the prior art tandem mills, the last stand arranged in the tandem mill was outfitted with rough work rolls through which the strip was rolled to roughen the strip surface to the appropriate roughness for reliable prevention of adhesion of the strip in the bell-type annealing installation.
In the prior art reversing cold rolling mills, the same sticking problem was solved in that a certain quantity of the strip was initially rolled out by blank or smooth work rolls of the reversing stands and stored. The smooth work rolls were then removed and replaced with work rolls having a suitable roughness. All of the temporarily stored coils of smooth strip then had rolled through a second pass in the rolling mill for applying the required roughness to prevent sticking. It is plain to see that the cost of this step was an enormous increase in production times which had a negative impact on the economy of the reversing cold rolling mill. In addition, as a result of the intermediate storage of the coils, rolling emulsion dried onto the surface of the strip and could be removed subsequently only with difficulty.
In both the prior art tandem cold rolling mills and the prior art reversing cold rolling mills, a deterioration in the evenness of the strip occurs as a result of the heat treating process in the bell-type annealing installation. This deterioration is accounted for by reducing the annealed strip after leaving the bell-type annealing installation in a flattening pass through a temper rolling mill provided especially for this purpose with only slight elongation of about 1-2%. The temper rolling mill works in dry operation and is set up following the bell-type annealing installation. In practice, the temper roll stand is used only for one pass per coil and therefore is not in use during most of the production time required for each coil of the metal strip.